NACE CP2 EXAM QUESTIONS AND
ANSWERS
oxidation - Answer loss of electrons, positive charge atoms (anode)
reduction - Answer gain of electrons, negative charged atoms (cathode)
forms of corrosion - Answer uniform, crevice, galvanic (dissimilar metals) if two metals
have to be couple then best to couple metals close together in the galvanic series,
pitting, intergranular, selective leaching (dezincification, graphitization), velocity
phenomena, environmental cracking (corrosion fatigue, hydrogen embrittlement, SCC
(Carbonates/bicarbonates)
High PH - Answer Low hydrogen, alkaline, easy polarization
Low PH - Answer high hydrogen, acidic, harder to polarize
High oxygen/High Hydrogen concentration - Answer harder to polarize, work at the
cathode only, called cathodic depolarizers.
factors affecting corrosion - Answer A. anything that affects polarization. (temp. etc...)
B. concentration cells (oxygen, temp, etc.) In an oxygen concentration cell, what is the
anode? (i.e. the area with more or less oxygen?) In a metal ion cell, which area is the
anode (i.e. the area with the greater of lower concentration)?
C. Anaerobic bacteria (MIC) Absence of oxygen, depolarizer
polarization - Answer a. corrosion current reduces with polarization
b. polarization increases with CP current applied
c. Occurs at surface of both anode and cathode.
shielding - Answer a. shorted casings
b. proximity of other structures
c. reinforced concrete
amphoteric materials - Answer corrode at low and high pH
on potential - Answer native + polarization + IR drop
polarized potential (off) - Answer native + polarization
,kirchoff's laws - Answer a. voltage (series circuits)
b. current (parallel circuits)
faraday's law - Answer W=KIT
relates weight loss of metal in a corrosion cell with time and current flow.
rate of corrosion - Answer directly proportional to current flow
cathodic protection limitations - Answer -shielding issues
-attenuation
-interference
-excessive current density
-contact with other metals (shorts)
measurement methods - Answer true voltage reading
voltmeter reading
% error calculations
effect of voltmeter resistance
IR correction methods
test stations - Answer allow electrical connection to structure for potential
measurements and bonds.
Spans allow current and direction (IR drop).
inistall during construction
pH - Answer measure of acidity(hydrogen ion concentration)
high pH is alkaline
low pH is acid
pH is a log function therefore each increase in pH is a factor of 10.
RECTIFIER - Answer - positive to anode
-negative to structure
- AC suppy
-AC circuit breaker
-Transformer (increase or decrease voltage)
-AC fuse
-rectifier bridge - diodes change AC to DC
-Voltmeter and Ammeter
-Surge Protection
-Filters
Esecondary = (Eprimary x Secondary turns) / primary turns
Reference electrode location - Answer the reference electrode should be placed as
close to the structure as practical. (underground piping or tanks- over the center of the
structure, multiple readings along the structure as required)
, internal surfaces of storage tanks, waterfront and offshore structures (as close to the
wall as possible)
impressed current vs sacrificial - Answer impressed current- higher current, better
control
sacrificial- no power required, less maintenance, easy to install, less land
AC considerations - Answer capacitance, inductance, and resistance
hazardous AC potential - 15 Vac
Safe method of connecting ground0 cable to ground then to pipe
arcing hazards
corrosion rates from AC (current density)
switching or pulse rectifiers
Reference cells - Answer CuCuSO4- most common, (soil, fresh water)
AgAgCL - seawater
Calomel- lab
Hydrogen - standard (lab)
zinc- stationary
Cathodic Protection - Answer protect the cathode
attempts to bring the cathode potential as negative as the anode potential
NACE criteria- what are the exceptions?
-high temperature
-bacteria
-sulfides
-acid environments
-dissimilar metals
Isolation Requirement - Answer confine protection to protected structure thus limiting
the current required for protection.
use for stray current with care
ANSWERS
oxidation - Answer loss of electrons, positive charge atoms (anode)
reduction - Answer gain of electrons, negative charged atoms (cathode)
forms of corrosion - Answer uniform, crevice, galvanic (dissimilar metals) if two metals
have to be couple then best to couple metals close together in the galvanic series,
pitting, intergranular, selective leaching (dezincification, graphitization), velocity
phenomena, environmental cracking (corrosion fatigue, hydrogen embrittlement, SCC
(Carbonates/bicarbonates)
High PH - Answer Low hydrogen, alkaline, easy polarization
Low PH - Answer high hydrogen, acidic, harder to polarize
High oxygen/High Hydrogen concentration - Answer harder to polarize, work at the
cathode only, called cathodic depolarizers.
factors affecting corrosion - Answer A. anything that affects polarization. (temp. etc...)
B. concentration cells (oxygen, temp, etc.) In an oxygen concentration cell, what is the
anode? (i.e. the area with more or less oxygen?) In a metal ion cell, which area is the
anode (i.e. the area with the greater of lower concentration)?
C. Anaerobic bacteria (MIC) Absence of oxygen, depolarizer
polarization - Answer a. corrosion current reduces with polarization
b. polarization increases with CP current applied
c. Occurs at surface of both anode and cathode.
shielding - Answer a. shorted casings
b. proximity of other structures
c. reinforced concrete
amphoteric materials - Answer corrode at low and high pH
on potential - Answer native + polarization + IR drop
polarized potential (off) - Answer native + polarization
,kirchoff's laws - Answer a. voltage (series circuits)
b. current (parallel circuits)
faraday's law - Answer W=KIT
relates weight loss of metal in a corrosion cell with time and current flow.
rate of corrosion - Answer directly proportional to current flow
cathodic protection limitations - Answer -shielding issues
-attenuation
-interference
-excessive current density
-contact with other metals (shorts)
measurement methods - Answer true voltage reading
voltmeter reading
% error calculations
effect of voltmeter resistance
IR correction methods
test stations - Answer allow electrical connection to structure for potential
measurements and bonds.
Spans allow current and direction (IR drop).
inistall during construction
pH - Answer measure of acidity(hydrogen ion concentration)
high pH is alkaline
low pH is acid
pH is a log function therefore each increase in pH is a factor of 10.
RECTIFIER - Answer - positive to anode
-negative to structure
- AC suppy
-AC circuit breaker
-Transformer (increase or decrease voltage)
-AC fuse
-rectifier bridge - diodes change AC to DC
-Voltmeter and Ammeter
-Surge Protection
-Filters
Esecondary = (Eprimary x Secondary turns) / primary turns
Reference electrode location - Answer the reference electrode should be placed as
close to the structure as practical. (underground piping or tanks- over the center of the
structure, multiple readings along the structure as required)
, internal surfaces of storage tanks, waterfront and offshore structures (as close to the
wall as possible)
impressed current vs sacrificial - Answer impressed current- higher current, better
control
sacrificial- no power required, less maintenance, easy to install, less land
AC considerations - Answer capacitance, inductance, and resistance
hazardous AC potential - 15 Vac
Safe method of connecting ground0 cable to ground then to pipe
arcing hazards
corrosion rates from AC (current density)
switching or pulse rectifiers
Reference cells - Answer CuCuSO4- most common, (soil, fresh water)
AgAgCL - seawater
Calomel- lab
Hydrogen - standard (lab)
zinc- stationary
Cathodic Protection - Answer protect the cathode
attempts to bring the cathode potential as negative as the anode potential
NACE criteria- what are the exceptions?
-high temperature
-bacteria
-sulfides
-acid environments
-dissimilar metals
Isolation Requirement - Answer confine protection to protected structure thus limiting
the current required for protection.
use for stray current with care
